Field
The present disclosure relates to medical devices and, more particularly, to methods and apparatus for spondylolysis repair.
Description of the Related Art
The human spine is a flexible weight bearing column formed from a plurality of bones called vertebrae. There are thirty-three vertebrae, which can be grouped into one of five regions (cervical, thoracic, lumbar, sacral, and coccygeal). Moving down the spine, there are generally seven cervical vertebrae, twelve thoracic vertebra, five lumbar vertebra, five sacral vertebra, and four coccygeal vertebra. The vertebrae of the cervical, thoracic, and lumbar regions of the spine are typically separate throughout the life of an individual. In contrast, the vertebra of the sacral and coccygeal regions in an adult are fused to form two bones, the five sacral vertebra which form the sacrum and the four coccygeal vertebra which form the coccyx.
In general, each vertebra contains an anterior, solid segment or body and a posterior segment or arch. The arch is generally formed of two pedicles and two laminae, supporting seven processes—four articular, two transverse, and one spinous. There are exceptions to these general characteristics of a vertebra. For example, the first cervical vertebra (atlas vertebra) has neither a body nor spinous process. In addition, the second cervical vertebra (axis vertebra) has an odontoid process, which is a strong, prominent process, shaped like a tooth, rising perpendicularly from the upper surface of the body of the axis vertebra. Further details regarding the construction of the spine may be found in such common references as Gray's Anatomy, Crown Publishers, Inc., 1977, pp. 33-54, which is herein incorporated by reference.
The human vertebrae and associated connective elements are subjected to a variety of diseases and conditions which cause pain and disability. Among these diseases and conditions are spondylolysis, spondylolisthesis, vertebral instability, spinal stenosis and degenerated, herniated, or degenerated and herniated intervertebral discs. Additionally, the vertebrae and associated connective elements are subject to injuries, including fractures and torn ligaments and surgical manipulations, including laminectomies.
One particular source of pain and disability is spondylolysis, otherwise known as pars fracture or pars defect, which is a fracture or dislocation of the pars interarticularis. The pars interarticularis is the bony mass between the facet joints, anterior to the lamina and posterior to the pedicle. With a pars fracture, the pars interarticularis is detached and there is a separation of the joints. These fractures are generally caused by mechanical stress and fatigue “stress” fractures caused by repetitive loading. It is reported that between 6% and 10% of the population have pars defects, with a higher prevalence among athletes. Spondylolysis can be treated conservatively by bracing, or by injections which do not themselves correct the condition but may relieve the associated pain. While some patients with spondylolysis do not require surgery, for others surgical intervention is necessary. One approach is full interbody fusion, which is typically associated with patients for whom the pars defect has caused or contributed to a spondylolysis of greater than grade 1, or where leg pain or weakness is present. Full interbody fusion is a high-profile, disruptive technique with significant operating and recovery times. Additionally, full body fusion is particularly inappropriate for younger patients, and for athletes of any age, as it results in loss of motion at one level.
Another surgical approach is direct repair of spondylolysis, without interbody fusion. Existing systems include a pedicle screw and hook fixation, pedicle screw and V-rod system, a cable-screw construct, or a direct insertion of a bone screw across the fracture (i.e., Buck's technique). Each of these techniques suffers from significant shortcomings. For example Buck's technique is an unfamiliar technique for surgeons and requires anchoring the screw in a thin portion of the vertebrae, thereby risking further fracture or dislocation of the bone screw. Pedicle screw and hook, pedicle screw and V-rod, or cable-screw constructs all require open surgery, with no option for minimally invasive surgery. Each also relies on complex hardware, with long operating times and long recovery times.
Notwithstanding the variety of efforts in the prior art, there remains a need for a fixation device for treatment of spondylolysis which provides improved locking force, which resists migration, and which can be easily and rapidly deployed via a minimally invasive approach.